MANUFACTURE OF NEAR-NET SHAPE TITANIUM ALLOY ARTICLES FROM METAL POWDERS BY SINTERING WITH PRESENCE OF ATOMIC HYDROGEN

摘要

Disclosed herein is a process that includes:
(a) forming a powder blend by mixing Commercially Pure (C.P.) titanium powder, one or more hydrogenated titanium powders containing around 3.4 to around 3.9 weight % of hydrogen (e.g., hydrogenated titanium powders available or referred to nominally as “titanium hydride” or TiH2), and one or more hydrogenated titanium powders containing around 0.2 to around 3.4 weight % of hydrogen, or a mixture of the hydrogenated titanium powders without the C.P. titanium powder,(b) consolidating the powder blend by either compacting the powder blend using die pressing, direct powder rolling, cold isostatic pressing, impulse pressing, metal injection molding, other room temperature consolidation method, or combination thereof, at a pressure in the range of around 400 to around 960 MPa, or loose sintering, to provide a green compact having a density lower than that of a green compact formed from only C.P. titanium powder, such that the subsequent sintering of said green compacts is promoted by an increased hydrogen content retained in the green compact which provides emission of hydrogen and a high partial pressure during subsequent cleaning and sintering steps,(c) heating the green compact to a temperature ranging from around 100° C. to around 250° C. at a heating rate≦around 15° C./min, thereby releasing absorbed water from the titanium powder, and holding the green compact at this temperature for a holding time ranging from around 10 to around 360 min, wherein the holding time and a thickness of the green compact are such that there is around 20 to around 24 min of holding time per every 6 mm of the thickness of the green compact,(d) forming β-phase titanium and releasing atomic hydrogen from the hydrogenated titanium by heating the green compact to a temperature of around 400 to around 600° C. in an atmosphere of hydrogen emitted by the hydrogenated titanium and holding the green compact at this temperature for around 5 to around 30 min thereby forming and releasing reaction water from the hydrogenated titanium powder,(e) reducing surface oxides on particles of the titanium powder by contact with atomic hydrogen released by heating of the green compact to a temperature of around 600 to around 700° C. and holding at this temperature for a holding time of around 30 to around 60 min sufficient to transform β-phase titanium into α-phase titanium while preventing dissolution of oxygen in the metallic body of the titanium particles and simultaneously providing maximum cleaning of titanium powders before forming closed pores,(f) diffusion-controlled chemical homogenizing of the green compact and densification of the green compact by heating to around 800 to around 850° C. at a heating rate of around 6 to around 8° C./min, followed by holding at this temperature for 30-40 min resulting in complete or partial dehydrogenation and more active shrinkage of titanium powder formed from the initial hydrogenated titanium powder to form a cleaned and refined compact,(g) heating the cleaned and refined green compact in vacuum at a temperature in the range of around 1000 to around 1350° C., and holding the cleaned and refined green compact at such temperature for at least around 30 minutes, thereby sintering titanium to form a sintered dense compact, and(h) cooling the sintered dense compact to form a sintered near-net shaped article.

主权项

1. A method for the manufacture of near-net shape titanium and titanium alloy articles from metal powders by sintering in the presence of atomic hydrogen comprising:
(a) forming a powder blend comprising mixing (1) Commercially Pure (C.P.) titanium powder, and (2) one or more of (i) one or more hydrogenated titanium powders containing around 3.4 to around 3.9 weight % of hydrogen, and (ii) one or more hydrogenated titanium powders containing around 0.2 to around 3.4 weight % of hydrogen, (b) consolidating the powder blend by either compacting the powder blend using die pressing, direct powder rolling, cold isostatic pressing, impulse pressing, metal injection molding, other room temperature consolidation method, or combination thereof, at a pressure in the range of around 400 to around 960 MPa, or loose sintering, to provide a green compact having a density lower than that of a green compact formed from only C.P. titanium powder, such that the subsequent sintering of said green compacts is promoted by an increased hydrogen content retained in the green compact which provides emission of hydrogen and a high partial pressure during subsequent cleaning and sintering steps, (c) heating the green compact to a temperature ranging from around 100° C. to around 250° C. at a heating rate around 15° C./min, thereby releasing absorbed water from the titanium powder, and holding the green compact at this temperature for a holding time ranging from around 10 to around 360 min, wherein the holding time and a thickness of the green compact are such that there is around 18 to around 24 min of holding time per every 6 mm of the thickness of the green compact, (d) forming β-phase titanium and releasing emitted atomic hydrogen from the hydrogenated titanium by heating the green compact to a temperature of around 400 to around 600° C. in an atmosphere of hydrogen emitted by the hydrogenated titanium and holding the green compact at this temperature for around 5 to around 30 min thereby forming and releasing reaction water from the hydrogenated titanium powder, (e) reducing surface oxides on particles of the titanium powder by contact with atomic hydrogen released by heating of the green compact to a temperature of around 600 to around 700° C. and holding at this temperature for a holding time of around 30 to around 60 min sufficient to transform β-phase titanium into α-phase titanium while preventing dissolution of oxygen in the metallic body of the titanium particles and simultaneously providing maximum cleaning of titanium powders before forming closed pores, (f) diffusion-controlled chemical homogenizing of the green compact and densification of the green compact by heating to around 800 to around 850° C. at a heating rate of around 6 to around 8° C./min, followed by holding at this temperature for around 20 to around 40 min resulting in complete or partial dehydrogenation and more active shrinkage of titanium powder formed from the initial hydrogenated titanium powder to form a cleaned and refined compact, (g) heating the cleaned and refined green compact in vacuum at a temperature in the range of around 1000 to around 1350° C., and holding the cleaned and refined green compact at such temperature for at least around 30 minutes, thereby sintering titanium to form a sintered dense compact, and (h) cooling the sintered dense compact to form a sintered near-net shaped article.